1. Field of the Invention
The present invention generally relates to telecommunication systems and more particularly to acoustic echo cancellation.
2. Description of the Related Art
In telecommunication systems (e.g. telephony and video conferencing systems), audio signals such as a user""s voice are transmitted to a loudspeaker in a remote location using a microphone. A microphone and a loudspeaker are provided at each location for sending and receiving audio signals. Acoustic coupling occurs in these systems whenever a microphone is placed where it can pick up the sounds from a loudspeaker in the same location. In which case, the user""s voice is transmitted to a loudspeaker in a remote location, picked up by a microphone in the remote location, and re-transmitted back to the loudspeaker in the user""s location, thereby resulting in the user hearing back his own voice (i.e. an echo). Acoustic coupling between microphones and loudspeakers is difficult to eliminate because microphones and loudspeakers are typically located in the same general area, such as in a conference room or a large hall.
Acoustic Echo Cancelers(xe2x80x9cAECxe2x80x9d) have been developed to eliminate echoes caused by acoustic coupling. AECs, in general, are well known; see for example: U.S. Pat. No. 4,965,822 (Williams); H. Yasukawa et al., xe2x80x9cAcoustic Echo Canceler with High Speech Quality,xe2x80x9d Institute of Electrical and Electronic Engineers (xe2x80x9cIEEExe2x80x9d) CH2396-0/87/0000-2125 (1987); A. Gilloire, xe2x80x9cExperiments With Sub-Band Acoustic Echo Cancelers For Teleconferencing,xe2x80x9d IEEE CH2396-0/87/0000-2141 (1987); J. Chen et al., xe2x80x9cA New Structure For Sub-Band Acoustic Echo Canceler,xe2x80x9d IEEE CH2561-9/88/0000-2574 (1988); and C. Breining et al., xe2x80x9cAcoustic Echo Control: An Application of Very-High Order Adaptive Filters,xe2x80x9d IEEE Signal Processing Magazine 1053-5888/99, pp. 42-69 (1999). All of the aforementioned references are incorporated herein by reference.
A typical AEC uses an adaptive filter to generate an echo estimate signal that is subtracted from the microphone""s output signal. If the echo estimate signal matches the echo embedded in the microphone""s output signal, the echo is canceled out (i.e. removed). The accuracy of the generated echo estimate signal is dependent on the AEC""s capability to change the coefficients of its adaptive filter to adapt to the echo. Thus, improving the capability of AECs to adapt to echoes is highly desirable.
The present invention relates to a method and associated apparatus for controlling an AEC. In one embodiment, distortion detectors are used to determine if an audio signal is distorted. If so, the AEC is prevented from incorrectly adapting its filter coefficients to the distorted audio signal. This allows the AEC to maintain a valid set of filter coefficients that can be rapidly adapted to cancel subsequent echoes.